1. Field of the Invention
The present invention relates to generating an output signal representing temperature. More particularly, the present invention relates to cold junction compensation for a transmitter which generates an output signal based on an input signal from a thermocouple.
2. Description of the Prior Art
In prior art transmitters, cold junction compensation has been achieved by thermally coupling a temperature sensing resistor to cold junction terminals. There is thermal resistance between the terminals and the sensing resistor. When rapid temperature changes occur around the terminals, transient temperature differences between the terminal and the sensing resistor cause transient errors in the cold junction compensation. Various techniques are known to reduce this error, such as providing a thermal mass around the cold junction terminals and the sensing resistor, or adding mass to the sensing resistor to match its thermal transient response to that of the cold junction as taught in U.S. Pat. No. 4,623,266 to Kielb.
However, improving transient temperature response by adding mass has the undesired effect of increasing size, weight and cost of the transmitter. As advances are made in reducing size and increasing accuracy in thermocouple converter circuits, these prior art arrangements impose significant limits on transmitter size and temperature conversion accuracy.
Therefore, there is a need to increase accuracy and reduce size of thermocouple terminals so that fuller advantage can be taken of improved converter accuracy. Also, if the size of the thermocouple terminals is reduced, corresponding reductions in the size of surrounding transmitter housings can be affected.